Have been on 10 Carnival cruises and never received a pin at the past guest party. We got a pin once on the Fascination in our cabin in early 2001 and haven't gotten anything on subsequent cruises.
They do have a little film now on the history of Carnival and showing all their ships, even the ones that aren't with the company any more. That was something that was new on our last cruise at the past guest party. Otherwise it is free selected drinks for about an hour.